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Abstract:

A nozzle valve gate for injecting hot plastics into an injection mold
includes a body having a passage for flow of the plastics to an outlet
and forming an actuator chamber. A nozzle part is connected to the body
and extends longitudinally to a nozzle tip having an injection aperture.
The nozzle part has a flow passageway connected to the plastics outlet
for conducting the plastics melt to the injection aperture and a machined
bore forming a guide passageway. A valve pin is movable in the guide
passageway between open and closed positions. A piston is connected to
the pin and is slidable in the actuator chamber. An elastomeric wiper
seal extends around the valve pin adjacent the machined bore, is wear
resistant, and can withstand high temperatures of at least 200° C.
A micro gap is formed between the pin and the machined bore.

Claims:

1. A nozzle valve gate apparatus for delivering and injecting hot
plastics material into an injection mold for molding a plastics product
or part, said nozzle valve gate apparatus comprising: a chamber forming
body having first passage means for flow of said hot plastics material
from a plastics inlet to at least one plastics outlet, said body forming
an actuator chamber; a nozzle part connected to said body and having a
longtiduinal axis, said nozzle part extending in the longitudinal
direction to a nozzle tip having an injection aperture for said hot
plastics material to flow into said injection mold, said nozzle part
forming second injection passage means operably connected to said at
least one plastics outlet for conducting said hot plastics material to
said injection aperture and forming a longitudinal guide passage
comprising a machined bore; a valve pin extending through said guide
passage and movable therein in the longitudinal direction between an open
position at which said hot plastics material can flow through said
injection aperture and a closed position which stops flow of the plastics
material through the injection aperture; a piston connected to said valve
pin, slidably mounted in said actuator chamber, and adapted to move said
valve pin between said open and closed positions by way of fluid pressure
in said actuator chamber during use of said valve gate apparatus; and an
elastomeric wiper seal extending around and engaging said valve pin
adjacent said machined bore, said wiper seal being made of wear resistant
material and being capable of withstanding operating temperatures for
said valve gate apparatus of at least 200.degree. C., wherein a micro gap
between 1 and 10 microns is formed between said valve pin and said
machined bore, and a zero gap is formed between said wiper seal and the
valve pin.

2. A nozzle valve gate apparatus according to claim 1 wherein said
chamber forming body is provided by a nozzle rear body, said nozzle part
is a nozzle shaft detachably connected to one end of said nozzle rear
body, a central holding cavity is formed in an end of said nozzle shaft
adjacent said nozzle rear body, and said wiper seal is arranged in said
central holding cavity.

3. A nozzle valve gate apparatus according to claim 2 wherein said wiper
seal is capable of withstanding operating temperatures for said valve
gate apparatus of at least 300.degree. C.

4. A nozzle valve gate apparatus according to claim 1 wherein said wiper
seal is made of polyimide with a molybdenum disulfide filler.

5. A nozzle valve gate apparatus according to claim 1 wherein said wiper
seal is made of PTFE with a boron nitrate filler.

6. A nozzle valve gate apparatus according to claim 1 wherein said wiper
seal is a polymer selected from the group consisting of PI, PEI, and
PEEK, said polymer containing a friction reducing filler.

7. A nozzle valve gate apparatus according to claim 2 including an
annular retainer mounted in the central holding cavity and acting to hold
said wiper seal in the central holding cavity.

8. A nozzle valve gate apparatus according to claim 7 wherein said
annular retainer is held in the holding cavity by a set screw and a
further wiper seal is held in said retainer by said set screw.

9. A hotrunner system for injecting plastics material into an injection
mold, said system comprising: a hotunner manifold having an inlet for
receiving melted plastics material and a plastics feed conduit connected
to said inlet, said manifold being adapted for operation at a desired
elevated temperature suitable for flow of said melted plastics material
through said manifold; a plurality of injection apparatus operatively
connected to respective outlets of said feed conduit, each injection
apparatus having (i) a nozzle device having a longitudinal axis and a
longitudinal injection passage extending to a nozzle tip, an elongate
valve pin extending through a machined guide bore formed in said nozzle
device and movable in the bore between an open position at which said
melted plastics can flow from the nozzle tip into the injection mold and
a closed position to stop the flow of said plastics materials from the
nozzle tip, and (iii) a piston connected to an end of the valve pin,
slidably mounted in an actuator chamber formed in the nozzle device, and
adapted to move said valve pin between said open and closed pistons by
way of fluid pressure in said actuator chamber during use of the
hotrunner system, and an elastomeric wiper seal extending around and
engaging said valve pin adjacent said guide bore, said wiper seal
providing a zero gap between the wiper seal and the valve pin and being
capable of withstanding operating temperatures for its respective
injection apparatus of at least 200.degree. C., wherein a micro gap
ranging between 1 and 10 microns is formed between said valve pin and
said guide bore.

10. A hotrunner system according to claim 9 wherein each nozzle device
comprises a nozzle rear body and a nozzle shaft connected to one end of
said nozzle rear body, a central seal cavity is formed in a rear end of
said nozzle shaft adjacent said nozzle rear body, and said wiper seal is
fixedly arranged in said seal cavity.

11. A hotrunner system according to claim 10 wherein each wiper seal is
capable of withstanding operating temperatures for its respective
injection apparatus of at least 300.degree. C.

12. A hotrunner system according to claim 9 wherein each wiper is made of
polyimide with a molybdenum disulfide filler.

13. A hotrunner system according to claim 9 wherein said wiper seal is a
polymer selected from the group consisting of PI, PEI, and PEEK, said
polymer containing a friction reducing filler.

14. A hotrunner system according to claim 10 including an annular
retainer member mounted in the central seal cavity and holding said wiper
seal in said central seal cavity.

15. A hotrunner system according to claim 14 wherein said retainer member
is held in said central seal cavity by a set screw threaded into the seal
cavity and a further wiper seal is mounted in said retainer member.

16. A nozzle valve gate apparatus for injecting hot plastics material
into an injection mold for molding a plastics product or part, said
nozzle valve gate apparatus comprising: an actuator mechanism having an
actuator chamber and a piston slidably mounted in said actuator chamber
and movable therein by fluid pressure in said actuator chamber during use
of said valve gate apparatus; an injection arrangement including an
injection nozzle having a longitudinal axis and extending in the
longitudinal direction to a nozzle tip having an injection aperture for
said hot plastics material to flow into said injection mold, said
injection nozzle forming an injection passage for conducting said hot
plastics materials from at least one inlet of the injection arrangement
to said injection aperture, said injection arrangement having a machined
guide bore extending in the longitudinal direction, a valve pin extending
through said guide bore and movable therein to open or close said
injection aperture, said valve pin being connected to said piston and
movable thereby, and an elastomeric wiper seal extending around and
slidably engaging said valve pin, said wiper seal being capable of
withstanding injection nozzle operating temperatures of at least
200.degree. C., being mounted in said injection arrangement adjacent said
guide bore, and being separated from said injection passage by at least a
section of said guide bore, wherein a micro gap is provided between the
valve pin and at least said section of the guide bore and a zero gap is
formed between said wiper seal and the valve pin.

17. A nozzle valve gate apparatus according to claim 16 wherein said
injection arrangement includes a heatable manifold connected to an end of
said injection nozzle located furthest from the nozzle tip, said guide
bore is formed in the manifold, and the wiper seal is mounted in a cavity
formed in said manifold.

18. A nozzle valve gate apparatus according to claim 17 including-an
annular retainer member mounted in said cavity and fixedly holding said
wiper seal in said cavity.

19. A nozzle valve gate apparatus according to claim 17 wherein said
actuator mechanism and said injection nozzle are mounted on opposite
sides of said manifold, said micro gap is in the range of 1 to 10
microns, and said wiper seal is formed with and contains a lubricating
filler.

20. A nozzle valve gate apparatus according to claim 16 wherein said
wiper seal is made of polyimide and is self-lubricating.

21. A nozzle valve gate apparatus according to claim 16 wherein said
wiper seal is a polymer selected from the group consisting of PI, PEI,
and PEEK, said polymer containing a friction reducing filler.

22. A nozzle valve gate apparatus according to claim 18 wherein said
injection arrangement includes a mounting plate mounted between said
manifold and said actuator mechanism, a portion of said retainer member
is mounted in a hole formed in the mounting plate, and said mounting
plate secures another portion of said retainer member in said cavity.

23. A hotrunner system for injecting plastics material into an injection
mold for molding plastics devices or parts, said system comprising: a
hotrunner manifold having an inlet for receiving melted plastics material
and a plastics feed conduit connected to said inlet, said manifold being
adapted for operation at a desired elevated temperature suitable for flow
of said melted plastics material through said manifold without
undesirable degradation, said manifold forming actuator chambers; a
plurality of nozzle members mounted on at least one side of said manifold
and each having a longitudinal axis, each nozzle member having an
injection passage operatively connected to a respective outlet of said
feed conduit and extending to a nozzle tip and having a longitudinal
guide passage formed therein, each guide passage comprising a machined
bore; a plurality of elongate valve pins each extending through a
respective one of the guide passages and movable therein between an open
position at which said melted plastics material can flow from the
respective nozzle tip into the injection mold and a closed position which
stops flow from the nozzle tip, a micro gap being formed between each
valve pin and its respective machined bore, said micro gap under normal
hotrunner system operating conditions helping to prevent hot melted
plastics material in the respective nozzle member from passing through
the micro gap into the adjacent actuator chamber; elastomeric wiper seals
each extending around a respective one of said valve pins adjacent its
respective machined bore, said wiper seals being made of wear resistant
material and being capable of withstanding operating temperatures of at
least 200.degree. C., wherein a zero gap is formed between each wiper
seal and its respective valve pin; and a plurality of pistons each
connected to a rear end of a respective one of the valve pins, slidably
mounted in an associated one of the actuator chambers, and adapted to
move its respective valve pin between said open and closed positions by
way of fluid pressure in the associated actuator chamber.

24. A hotrunner system according to claim 23 wherein said nozzle members
are mounted on two opposite sides of said manifold and the or each nozzle
member on one side is aligned in a back-to-back manner with a respective
nozzle member on the opposite side and each aligned pair of nozzle
members is associated with one of the actuator chambers and aligned
therewith in the longitudinal direction of the nozzle members, the one
actuator chamber containing two pistons, one for each of the nozzle
members of the aligned pair.

25. A hotrunner system according to claim 23 wherein each valve pin
actuator is a pneumatic actuator and gas bores are formed in said
hotrunner manifold for delivering pressurized air or gas to or from each
actuator chamber.

26. A hotrunner system according to claim 23 wherein each nozzle member
is formed with a transversely extending additional passage that
intersects the machined bore of the nozzle member at a location spaced
from the adjacent actuator chamber, said additional passage allowing any
gases on plastics melt residue that has entered the machined bore to
escape.

27. A hotrunner system according to claim 23 wherein said pistons and
cylindrical walls of the manifold forming said actuator chambers are
machined to close tolerances so as to form a micro gap between a
peripheral wall of each piston and the adjacent cylindrical wall of the
associated actuator chamber.

28. A hotrunner system according to claim 23 wherein the cylindrical wall
of each actuator chamber has a machined nitride surface which is harder
than said peripheral wall of the associated piston.

Description:

[0001] This invention relates to nozzle valve gate apparatus for injecting
hot plastics material into an injection mold for molding plastic products
or parts and also to hotrunner systems for injecting plastics material
into an injection mold.

BACKGROUND OF THE INVENTION

[0002] Similar plastic parts are commonly produced in injection molds with
single or multiple cavities. In the case of an injection molding machine
wherein the mold has multiple cavities, it is known to use a hotrunner
system to deliver the hot plastics material or melt from a melt
plastification barrel of the machine to the cavities in the mold. The
hotrunner system provides the plastic melt at a defined. melt pressure
and a controlled melt temperature to each mold cavity. In order to
accomplish this objective, the hotrunner system commonly employs a heated
manifold through which melt conduits extend and heated injection nozzles.

[0003] Nozzle valve gates are used in the aforementioned melt distribution
systems to control the opening and closing of gate orifices, that is, the
orifices that open into each mold cavity and through which the melt is
delivered. The valve gate is a positive shut off device that has an open
and closed position. At the beginning of melt injection, a valve pin of
the valve gate opens the orifice in order to allow the plastic melt to
fill the adjacent cavity. In addition, after the cavity has been filled,
the gate orifice remains open during a packing phase which relies on
packing pressure to control the quality of the plastic part. While the
thermoplastic melt starts to solidify during the packing phase, the valve
gate closes the orifice to achieve a clean gate mark on the plastic part
surface and to avoid stringing or drooling of melt through the gate from
the hotrunner system while the mold opens for part injection.

[0004] A melt channel or passage is formed in the nozzle of the valve gate
to deliver the hot plastics melt to the gate orifice. Movement of the
valve pin inside this melt channel is generally an open and closed stroke
in the axial or longitudinal direction of the nozzle. The valve pin is
actuated between open and closed positions by means of a valve actuator
that is connected to a rear end of the valve pin. With known hotrunner
systems, the valve actuator is commonly located externally of the heated
components of the hotrunner system (for example, the manifold) because
the commonly used valve actuators are not functional at the usual melt
processing temperature of thermoplastics materials which is between 200
and 450° C. Generally pneumatic and hydraulic valve actuators are
provided with seals between the pistons and their respective cylinders
that operate only below 200° C. Also, electromechanic actuators
require a low ambient temperature of less than 200° C. It will be
understood that a heated melt distribution system or hotrunner system
inside a valve gate mold can, depending on the location of the actuators,
affect the valve actuators by heat conductivity, radiation and
convection. Because of this effect, valve actuators are commonly
positioned at a sufficient distance from the heated surface of the melt
distribution manifold and the injection nozzle to keep them within their
operating temperature range, which is preferably below 100° C.
Known valve pin actuators can be physically separated from the heated
manifold and the injection nozzle or nozzles by various means which allow
the actuators to be located in a remote location where the actuator
temperature can be maintained below 100° C. In addition to this
thermal separation from the hotrunner manifold and the nozzles, it is
known to provide for direct or indirect cooling of the actuators, Thus a
cooling circuit within the injection mold can be directly or indirectly
connected with the actuator to withdraw heat from the actuator.

[0005] It is also known to provide injection molds with a high number of
cavities for making small plastic parts and it is advantageous to make
such a mold as compact as possible. However, it is difficult and costly
to integrate valve actuators with an effective cooling system in a
compact mold of this type. Generally, valve pin actuators require
considerable space inside an injection mold and they can add to the
overall stack height of the mold. Moreover, forming cutout spaces for the
actuators and bores or cutouts for cooling lines as well as air,
hydraulic, or electric lines weakens the mold plate structure that has to
support the substantial forces of the melt injection pressure inside the
mold cavities and the clamping force in the molding machine.

[0006] U.S. Pat. No. 5,948,448 issued Sep. 7, 1999 to Eurotool, Inc.,
describes a hotrunner system for injecting hot plastics material into an
injection mold that includes a thermally insulated manifold with a
plastics flow channel extending therethrough to a nozzle part. An
elongated valve pin extends through the manifold and through the nozzle
and it is adapted to open or close an injection aperture. The head of the
pin is connected to an actuator located above the manifold and on the
side thereof opposite the nozzle member. The valve pin is slidably
mounted in an aperture formed in a valve seal bushing which is screwable
fixed within a complementary bore in a top surface of the manifold.

[0007] U.S. Pat. No. 6,159,000 issued Dec. 12, 2000 to Husky Injection
Molding Systems Ltd. describes a hotrunner valve gated injection molding
device which directs melt from a melt channel to a melt cavity. A guide
sleeve is positioned at the gate end of the nozzle body and surrounds a
valve stem in order to guide the valve stem inside the guide sleeve and
to provide a sealing device at the gate end of the nozzle body. In this
known system, the actuator for the valve pin is mounted in a valve plate
through which the nozzle body extends and that is separate from the
hotrunner manifold. The guide sleeve at the forward end of the nozzle
assembly may be made of any high resistant tool steel and can be a
nickel/chrome tool steel with a gas nitriding surface treatment to harden
the surface, or a tool steel having hard wearing properties. There can be
a close tolerance sliding engagement of the valve stem inside the guide
sleeve which is said to inhibit leaking of plastic melt through the bore
in the sleeve.

[0008] There is disclosed herein a novel valve gate apparatus for
delivering and injecting hot plastics material into an injection mold.
This valve gate is provided with an elastomeric wiper seal extending
around and engaging the valve pin adjacent a machined guide bore. This
wiper seal is made of a wear resistant material and is capable of
withstanding operating temperatures for the valve gate apparatus of at
least 200° C.

SUMMARY OF THE DISCLOSURE

[0009] According to one embodiment of the present disclosure a nozzle
valve gate apparatus for delivering and injecting hot plastics material
into an injection mold for molding a plastics product or part includes a
chamber forming body having a first passage arrangement for flow of the
hot plastics material from a plastics inlet to at least one plastics
outlet. This body forms an actuator chamber. A nozzle part is connected
to the body and has a longitudinal axis. This nozzle part extends in the
longitudinal direction to a nozzle tip having an injection aperture for
the hot plastics material to flow into the injection mold. The nozzle
part forms a second passage arrangement operably connected to the at
least one plastics outlet for conducting the hot plastics material to the
injection aperture and forms a longitudinal guide passage comprising a
machined bore. A valve pin extends through the guide passage and is
movable therein in the longitudinal direction between an open position at
which the hot plastics material can flow through the injection aperture
and a closed position which stops flow of the plastics material through
the injection aperture. A piston is connected to the valve pin, is
slidably mounted in the actuator chamber, and is adapted to move the
valve pin between the open and closed positions by means of fluid
pressure in the actuator chamber during use of the valve gate apparatus.
An elastomeric wiper seal extends around and engages the valve pin
adjacent the machined bore. This wiper seal is made of wear resistant
material and is capable of withstanding operating temperatures for the
valve gate apparatus of at least 200° C., A micro gap between 1
and 10 microns is formed between the valve pin and the machined bore and
a zero gap is formed between the wiper seal and the valve pin.

[0010] According to another embodiment of the present disclosure, a nozzle
valve gate for injecting hot plastics material into an injection mold for
molding a plastics product or part includes an actuator mechanism having
an actuator chamber and a piston slidably mounted in the chamber and
movable therein by fluid pressure in the actuator chamber during use of
the valve gate apparatus. The valve gate apparatus also has an injection
arrangement that includes an injection nozzle having a longitudinal axis
and extending in the longitudinal direction to a nozzle tip having an
injection aperture for the hot plastics material to flow into the
injection mold. This injection nozzle forms an injection passage for
conducting the hot plastics material from at least one inlet of the
injection arrangement to the injection aperture. The injection
arrangement has a machined guide bore extending in the longitudinal
direction. A valve pin extends through the guide bore and is movable
therein to open or close the injection aperture. The valve pin is
connected to the piston and movable thereby. An elastomeric wiper seal
extends around and slidably engages the valve pin. This seal is capable
of withstanding injection nozzle operating temperatures of at least
200° C. and is mounted in the injection arrangement adjacent the
guide bore. The seal is separated from the injection passage by at least
a section of the guide bore. A micro gap is provided between the valve
pin and at least the aforementioned section of the guide bore and a zero
gap is formed between the wiper seal and the valve pin.

[0011] In one version of this valve gate apparatus the injection
arrangement includes a heatable manifold connected to an end of the
injection nozzle located furthest from the nozzle tip. The guide bore is
formed in the manifold and the wiper seal is mounted in a cavity formed
in the manifold.

[0012] According to a further embodiment of the disclosure, a hotrunner
system for injecting plastics material into an injection mold includes a
hotrunner manifold having an inlet for receiving melted plastics material
and a plastics feed conduit connected to the inlet. The manifold is
adapted for operation at a desired elevated temperature suitable for flow
of the melted plastics material through the manifold. The hotrunner
system has a plurality of injection apparatus operatively connected to
respective outlets of the feed conduit. Each injection apparatus has a
nozzle device having a Longitudinal axis and a longitudinal injection
passage extending to a nozzle tip. An elongate valve pin extends through
a machine guide bore formed in the nozzle device and movable in the bore
between an open position at which the melted plastics can flow from a
nozzle tip into the injection mold and a closed position to stop the flow
of the plastics material from the nozzle tip. Each injection apparatus
also has a piston connected to an end of the valve pin, slidably mounted
in an actuator chamber formed in a nozzle device, and adapted to move the
valve pin between the open and closed positions by means of fluid
pressure in the actuator chamber during use of the hotrunner system. An
elastomeric wiper seal extends around and engages the valve pin adjacent
the guide bore. The wiper seal provides a zero gap between the wiper seal
and the valve pin and is capable of withstanding operating temperatures
for its respective injection apparatus of at least 200° C. A micro
gap ranging between 1 and 10 microns is formed between the valve pin and
the guide bore.

[0013] In one exemplary version of this hotrunner system, the nozzle
device includes a nozzle rear body and a nozzle shaft connected to one
end of the rear body. A central seal cavity is formed in a rear end of
the nozzle shaft adjacent the rear body and the wiper seal is fixedly
arranged in this seal cavity.

[0014] According to yet another embodiment of the hotrunner system of this
disclosure, the hotrunner system for injecting plastics material into an
injection mold for molding plastic devices or parts includes a hotrunner
manifold having an inlet for receiving melted plastics material and a
plastics feed conduit connected to the inlet. The manifold is adapted for
operation at a desired elevated temperature suitable for flow of the
melted plastics material through the manifold without undesirable
degradation. This manifold forms actuator chambers. A plurality of nozzle
members are mounted on at least one side of the manifold and each has a
longitudinal axis. Each nozzle member has an injection passage
operatively connected to a respective outlet of the feed conduit and
extending to a nozzle tip. Also each nozzle member has a longitudinal
guide passage formed therein and comprising a machined bore. A plurality
of elongate valve pins each extend through a respective one of the guide
passages and each is movable therein between an open position at which
the melted plastics material can flow from the respective nozzle tip into
the injection mold and a closed position which stops flow from the nozzle
tip. A micro gap is formed between each valve pin and its respective
machined bore and this micro gap under normal hotrunner system operating
conditions helps to prevent hot melted plastics material in the
respective nozzle member from passing through the micro gap into the
adjacent actuator chamber. Elastomeric wiper seals each extend around a
respective one of the valve pins adjacent its respective machined bore.
The wiper seals are made of wear resistant material and are capable of
withstanding temperatures of at least 200° C. A zero gap is formed
between each wiper seal and its respective valve pin. A plurality of
pistons are each connected to a rear end of a respective one of the valve
pins. Each piston is slidably mounted in an associated one of the
actuator chambers and each is adapted to move its respective valve pin
between the open and closed positions by means of fluid pressure in the
associated actuator chamber.

[0015] In one version of this hotrunner system, the nozzle members are
mounted on two opposite sides of the manifold and each nozzle member on
one side is aligned in a back-two-back manner with a respective nozzle
member on the opposite side.

[0016] These and other aspects of the nozzle valve gate apparatus and
hotrunner systems of the present disclosure will become more readily
apparent to those having ordinary skill in the art from the following
detailed description taken in conjunction with the drawings provided
herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] So that those having ordinary skill in the art to which the present
disclosure pertains will more readily understand how to make and use the
subject invention, exemplary embodiments thereof will be described in
detail herein below with reference to the drawings, wherein:

[0018] FIG. 1 is a longitudinal cross-section of a hotrunner molding
system, this view being partially broken away on the left side for sake
of illustration;

[0019] FIG. 2 is a transverse cross-section of the hotrunner molding
machine of FIG. 1 with a portion of the machine on the right side being
omitted for ease of illustration;

[0020] FIG. 3 is an exploded view showing the components of a nozzle valve
gate used in the machine of FIGS. 1 and 2;

[0021] FIG. 4 is an end view of a nozzle rear body used in the nozzle
valve gate of FIG. 3;

[0022] FIG. 5 is a longitudinal cross-section of the nozzle valve gate
taken along the line V-V of FIG. 4;

[0023] FIG. 6 is a transparent, perspective view of a manifold plate that
can be used in a hotrunner system of the present disclosure;

[0024] FIG. 7 is a partial, longitudinal cross-section of the hotrunner
molding machine of FIG. 1, this view showing a cavity plate on the bottom
side in a separated position in order to allow access to and disassembly
of a nozzle valve gate;

[0025] FIG. 8 is a top view of a nozzle valve gate apparatus, this view
showing the top of a nozzle valve gate actuator and the cavity plate in
which the valve gate is mounted;

[0026] FIG. 9 is a cross-sectional view taken along the line IX-IX of FIG.
8 with a portion of the left side of the cavity plate broken away for
ease of illustration;

[0027] FIG. 10 is another cross-sectional view taken along the line X-X of
FIG. 8;

[0028] FIG. 11 is a further cross-sectional view taken along the line
XI-XI of FIG. 8;

[0029] FIG. 12 is a longitudinal cross-sectional view of another
embodiment of a hotrunner molding machine, this embodiment having
actuator chambers located in the manifold;

[0030] FIG. 13 is a transverse cross-section of the molding machine of
FIG. 12, this view being taken along the line XIII-XIII of FIG. 12;

[0031] FIG. 14 is a cross-section of another embodiment of a hotrunner
molding machine, this embodiment being similar to that of FIG. 12 but
having nozzle members on opposite sides of the manifold;

[0032] FIG. 15 is a vertical cross-section through another embodiment of a
combination of valve gate and manifold, the combination having a top
mounted valve pin actuator; and

[0033] FIG. 16 is a cross-sectional detail view of the circled area D of
FIG. 15.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0034] Shown in FIGS. 1 and 2 is a partially illustrated hotrunner system
10 for injecting plastics material from a plasticiser unit into an
injection mold for molding plastic devices or parts. A barrel of a
plasticiser unit is shown in FIG. 6 and is indicated at 12. It will be
appreciated that the barrel and the plasticiser unit are of standard
construction and are well known in the manufacture of plastic products.
FIG. 6 illustrates the barrel connected to one side edge of a manifold
plate 14, a cross-section of which is shown in FIGS. 1 and 2. The barrel
is typically heated to the required temperature for the particular
plastics material being used by heaters such as electrical heaters. The
manifold plate itself is heated to an elevated temperature suitable for
conducting the melted plastics material without significant thermal
degradation by electric heaters (not shown). A plurality of injection
apparatus 16 are mounted in the hot runner molding machine with FIG. 1
showing four of these apparatus, two on each side of the manifold plate
plus an additional four cavities in which four further apparatus can be
mounted. Each of these apparatus is mounted to a downstream end of a
plastics feed conduit indicated generally at 18. Each injection apparatus
is in the form of a nozzle device having a longitudinal axis that extends
perpendicular to the adjacent surface of the manifold plate. Each
injection apparatus has a longitudinal injection passage 20, a portion of
which can be seen in FIG. 5. This passage extends to a nozzle tip 22
which can be of standard construction. Each injection apparatus also has
an elongate valve pin 24 extending through a longitudinal guide passage
formed in a nozzle device. This passage is indicated at 26 in FIG. 5. The
valve pin is movable in this passage in the direction of the longitudinal
axis between an open position at which the melted plastics material can
flow from the nozzle tip into the injection mold and a closed position to
stop the flow of the plastics material from the nozzle tip. The valve
pins are shown in the closed position in FIGS. 1 and 2 while FIG. 7 shows
the valve pin indicated at 24' in the open position. A cylindrical piston
28, which in an exemplary embodiment is made of tool steel is connected
to a rear end of the valve pin and is slidably mounted in an actuator
chamber 30 which is formed in the nozzle device. The piston is adapted to
move the valve pin 24 of each injection apparatus between the open and
closed positions by means of fluid pressure in the actuator chamber 30
during use of the hotrunner system.

[0035] Other major components of the hotrunner molding machine of FIGS. 1
and 2 include two cavity plates 32 and 34 located at the top and at the
bottom of the machine as illustrated in these figures. Each plate is
formed with stepped cavities 36 in each of which is mounted a portion of
a respective one of the injection apparatus 16. In particular each of
these cavities can be formed with an annular shoulder at 38 which engages
an annular flange 40 formed on annular mold section 42 into which a
section of the injection apparatus extends. Located between the two
cavity plates are two, similar manifold mold plates 44, 46 which are held
against one another under pressure applied through the cavity plates.
Formed between the two mold plates is a manifold cavity 48 with only a
left portion of this cavity being shown in FIG. 2. The manifold plate 14
is mounted centrally in this cavity as shown so that there is an
insulating air gap 50 extending completely around the manifold plate.
Furthermore it will be understood by those skilled in the hotrunner art
that coolant passageways (not shown) can be formed in the cavity plates
32, 34 which are typically maintained at a temperature in the range of
200 to 400° C. The actual temperature selected in this range will
depend upon the particular type of plastic being molded. Additional
coolant passages (not shown) can be formed in the mold plates 44, 46. A
suitable coolant is circulated through these passages to maintain these
plates at the desired temperature for operation of the mold apparatus and
the hotrunner system. Mold cavities 52 are typically formed in the mold
inserts or mold sections 42 that are secured in the cavity plates so the
mold apparatus can be used to make the desired plastics parts.

[0036] Turning now to the components which make up a nozzle valve gate
apparatus for the hotrunner system, FIG. 3 shows these components
separated from each other for ease of understanding. At the top of FIG. 3
is a nozzle rear body 54 formed with an end flange 56 that extends
radially outwardly. Formed in this rear body is the actuator chamber 30
which has a cylindrical shape and which is surrounded by a cylindrical
wall 58. There is also a coil heater 60 which can be electrically
operated and which, as shown in FIG. 5, extends around the cylindrical
outer wall of the rear body 54. This heater is used to maintain the rear
body at the required elevated temperature for the hot plastics material
flowing through the rear body. The injection apparatus further includes a
spring elastic nozzle support sleeve 62 which has a cylindrical exterior
and defines a cylindrical passage sized to extend about the heater 60. An
opening can be provided at 64 for passage of an electrical connector 66.
Located in the actuator chamber is the piston 28 which has a central
axial passage into which an upper end section of the valve pin 24
extends. The exemplary pin shown has an end flange 68 which acts to hold
the end of the valve pin in the piston. This end is locked in the piston
by means of a set screw 70. The threads on the set screw cooperate with
threads formed above the recess in the upper end of the piston to hold
the set screw firmly in place. The valve pin extends through a nozzle
part or shaft 72 which has the central, longitudinal guide passage 26
formed therein that guides the movement of the valve pin. The illustrated
exemplary nozzle part or shaft 72 has a wider end section 76, which is
adjacent the rear body 54, and a narrower nozzle section 78. The wider
end section 76 is formed with a plurality of screw holes 80 through which
extend longitudinally bolts 82. In the illustrated embodiment there are
four of these bolts and these are threaded into holes 85 formed in the
rear body 54. In this way the nozzle shaft is detachably but firmly
connected to the rear body. Moreover it will be seen that this
arrangement allows the nozzle shaft to be detached from the rear body
from the nozzle tip end of the injection apparatus for ease of
maintenance, etc.

[0037] Also shown in FIG. 3 is a cylindrical, hollow nozzle heater 86
which extends around the nozzle section 78 and is used to maintain this
section at the desired elevated temperature. The heater is held in place
by a heater retainer ring 88 which is a split ring which fits into groove
90 formed near the end of the nozzle section 78. Mounted in the nozzle
section 78 is a nozzle tip 92 which has a threaded exterior 94. These
threads engage internal threads in the nozzle section 78 for attachment
of the nozzle tip. FIG. 5 shows the valve pin in the open position at
which melted plastics material can flow through injection passage 20 and
can flow from the aperture 95 formed in the nozzle tip into the injection
mold. Forward movement of the piston will cause a corresponding downward
movement of the valve pin to the closed position which is shown in FIGS.
1 and 2. In this position the flow of the plastics material from the
nozzle tip is stopped completely.

[0038] Also visible in FIG. 5 are air passageways for delivering
pressurized dry air to and from the actuator chamber. These passageways
are formed in the rear body or chamber forming body 54 and include a
longer passageway 96 that extends from the top end of the rear body to a
point adjacent the bottom end of the actuator chamber and a shorter
passageway 98 that extends from the top end of the rear body to the top
of the actuator chamber 30. Also visible in FIGS. 4 and 5 is an opening
100 for the flow of hot plastics material into the injection apparatus
from the feed conduit 18 formed in the manifold plate. In the injection
apparatus shown, an injection passage for the hot plastics material
extends through the length of both the nozzle rear body 54 and the nozzle
part or shaft 72. This injection passage which includes the passage 20
splits into sub-passageways 102 and 104 formed in the nozzle rear body,
these sub-passageways during use of the hotrunner system diverting melted
plastics material around the actuator chamber 30. In the illustrated
embodiment there are two of these sub-passageways located on opposite
sides of the actuator chamber. It is possible for there to be more than
two sub-passageways distributed about the circumference of the chamber
and it is also possible for there to be only one flow passage that
extends around the actuator chamber and is formed in the cylindrical wall
of the body 54.

[0039] It will be seen from FIGS. 1 and 2 that each injection apparatus
including the actuator chamber 30, its piston 28 and the valve pin are
mounted on a side of the manifold or manifold plate 14 facing the
injection mold which is maintained at an elevated temperature for the
flow of the plastics material. In addition the actuator for the valve pin
including the nozzle rear body 54 and the piston are themselves at an
elevated temperature because of the flow of hot plastics material through
the sub-passageways in the rear body 54. Because of these elevated
operating temperatures, the piston 28 and the section of the injection
apparatus forming the actuator chamber 30 (that is the nozzle rear body
54) are machined to close tolerances to as to form a micro-gap between
peripheral wall 106 (see FIG. 3) of the piston and the adjacent wall 58
of the actuator chamber in the range of 1-10 microns (the μm). Because
of this micro-gap there is no need for fluid seals between the piston and
the wall 58. As a result the nozzle device and its piston provide a valve
pin actuator able to operate within plastic injection temperatures
ranging between 200 and 400° C. Note the "micro-gap" referred to
herein is the measured gap formed between the wall of the piston and the
wall of the actuator chamber when the walls are in contact with each
other on one side of the actuator. Thus the "micro-gap" is measured at a
point diametrically opposite the contact point of the two walls. It is
this distance which ranges between 1 and 10 microns.

[0040] In the illustrated hotrunner system, the valve pin actuator is a
pneumatic actuator operating on pressurized air, this pressurized air
being delivered through gas bores 108 formed in the hotrunner manifold
plate 14. A gridwork of gas bores can be seen in the transparent view of
FIG. 6. These bores can include pairs of larger, parallel bores 110 that
extend across the width of the manifold plate. These bores can be open at
one end for connection to pressurized gas lines and can be plugged at
their opposite ends, these plugs being indicated at 112. Further,
longitudinally extending gas bores can be provided at 114, these bores
intersecting the bores 110. The bores 114 can be connected to further
pressurized air lines (not shown) at each end of the manifold plate.

[0041] Because of the provision of a micro-gap between the peripheral wall
of the piston and the adjacent wall of the actuator chamber, the piston
does not have a greater co-efficient of thermal expansion than the
cylindrical wall 58 of the actuator chamber. In an exemplary version of
the actuator, the piston and the adjacent wall of the actuator chamber
have approximately the same co-efficient of thermal expansion. As shown
in FIGS. 1 to 3, the piston chamber or actuator chamber 30 is a
cylindrical precision bore with its open end facing towards the front
piece of the nozzle, that is, the nozzle part or shaft 72. The piston and
the cylindrical wall of the actuator 30 allow a low friction movement and
the micro-gap between them prevents air leak and pressure drop and
consequently avoids undesirable loss of valve pin force. The piston 28
and the wall 58 of the actuator chamber can be either hardened metal or
ceramic. In one sample embodiment, the piston is made of tool steel or
machine steel and the adjacent wall of the actuator chamber has a
machined nitride surface which is harder than the peripheral wall of the
piston. Alternate possible surfaces of the piston and/or the wall of the
actuator chamber are surfaces with physical vapour deposition (PVD) or
CVD enhancement. It will be appreciated that physical vapour deposition
on the peripheral wall of the piston can provide lubricant at the high
operating temperatures of the hot runner system. Also to provide
desirable lubrication the wall 58 of the actuator can be impregnated with
a high temperature dry lubricant in a manner known per se. The process
for providing lubricant by means of physical vapour deposition can, for
example, use TiN or CrN which is deposited in a vacuum on the surface by
plasma. The surface is bombarded with argon gas in an inert atmosphere.

[0042] It is also possible to construct the piston 28 of ceramic material
which has a lower co-efficient of expansion. In this embodiment, the
cylindrical surface of the actuator chamber can be made of tool steel.
Another alternative for the piston 28 is molybdenum TZM alloy, an alloy
which is 98% molybdenum and which is self-lubricating. If a piston of
this material is used, the cylindrical surface of the actuator chamber
can be made of tool steel which has a slightly higher co-efficient of
expansion than the molybdenum alloy of the piston.

[0043] In one embodiment of the actuator for the valve pin there is at
least a 10 Rockwell difference between the hardness of the piston
material and the hardness of the wall of the actuator chamber. The piston
28 is made of the softer material since it is easier to replace when it
becomes worn.

[0044] With respect to the air pressure required to operate the actuator
of each injection apparatus, the air pressure delivered to the actuator
chamber can be in the 100 to 120 PSI range, which is a standard level of
pressurized air that can be provided by a compressor. If a higher level
of pressurized air is required for operation of the injector apparatus,
the air pressure can be amplified, for example to overcome high injection
pressure that is acting on the front end of the valve pin. A typical
valve pin in a system such as that shown in FIGS. 1 and 2 has the
diameter ranging between 2.5 and 4 mm and can be used to open and close a
valve gate orifice 95 having a diameter of 1-2 mm.

[0045] FIG. 7 illustrates the front access capability of the valve gate
nozzle when the mold cavity plate 34 is removed. As shown in FIG. 7, the
molding machine allows the cavity plate 34 to be separated a sufficient
distance from the adjacent mold plate 46 to allow ready access to the
injection apparatus 16 that extend between these two plates. The same is
true of the other cavity plate 32 and its adjacent mold plate 44. It will
be seen that the present hotrunner system as illustrated in FIGS. 1, 2
and 7 provides accessibility from the cavity side of the mold. In other
words when the cavity plate 32 or 34 is removed as shown in FIG. 7, each
hotrunner nozzle on its side of the manifold has front exposure. This
easy access for maintenance allows servicing the nozzle tip, the nozzle
heater 86 and its thermal couple, the valve pin 24 and the valve pin
actuator including the piston while the mold remains inside the machine.
This access is unlike other valve pin actuators that are conventionally
mounted on the side of the nozzle or entirely at the opposite backside of
the manifold or even traditionally in the top clamp plate of the mold. In
these prior art arrangements, access for maintenance and repairs can
require the removal of the mold from the molding machine and this results
in considerable downtime.

[0046] FIGS. 8 to 11 illustrate an embodiment of the present disclosure
wherein the molding apparatus has only a single valve gate nozzle or
injection apparatus which is not attached to a melt distribution
manifold. This nozzle valve gate apparatus, which is indicated generally
at 130, is suitable for injecting hot plastics material into an injection
mold for molding a plastics product or part. The drawings illustrate a
nozzle valve gate 132, a bottom section of which is mounted in a cavity
plate 134 of rectangular shape. The plate has a top surface 136 in which
is formed a cavity for receiving the nozzle valve gate. A bottom surface
of the gate is formed with an orifice 95 that can be opened or closed by
the valve pin 24. As in the embodiment of FIGS. 3 to 5, the nozzle valve
gate has a nozzle rear body or chamber forming body 54 which forms an
actuator chamber 30. A piston 28 is slidably mounted in this chamber and
is connected to the top end of the valve pin using a threaded set screw
70. An electric coil heater 60 extends around the rear body and another
electric heater 86 extends around the nozzle shaft 72 which forms a guide
passageway for the valve pin. The nozzle valve gate or injection
apparatus is bolted to the plate 134 by means of a mold locating ring 140
through which extends a top section of the nozzle rear body 54. As shown
in FIG. 11, the mold locating ring 140 fits snugly within a counterbore
formed in a machine clamp plate which is maintained at a relatively cool
temperature. Also illustrated in FIG. 11 is the lower portion of a
machine nozzle of the molding machine, this machine nozzle being
indicated at 144. The outlet of the machine nozzle injects hot plastics
material into the top opening 100 of the injection nozzle.

[0047] Pressurized air to move the piston 28 in the actuator chamber is
provided through two elongate pipes or air lines 146, 148, each provided
with a fitting 150 for attachment purposes. The air line 148 is
operatively connected to internal gas passage 152 which is relatively
short and delivers air to the bottom side of the piston. The other air
line 146 is operatively connected to a longer internal gas passage 154
which is able to deliver air to the topside of the piston. Each air line
can be provided with a reduced diameter end section which is externally
threaded for connecting the air line to the nozzle shaft 72. The
pressurized air flow through the air lines 146, 148 is controlled by
five/three position solenoid valves of known construction. Pressurized
gas is delivered through the air line 148 in order to move the valve pin
to the open position allowing plastics melt to be injected into the mold
cavity. Air at the top of the actuator chamber can escape from the
chamber through the air line 146. In order to close the valve gate,
pressurized air is delivered through the air line 146 to the top end of
the actuator chamber which causes the valve pin to move to the closed
position.

[0048] With reference now to FIGS. 8 and 10, there are shown therein
mounting screws 156 which are used to detachably connect the mold
locating ring 140 to the cavity plate 134. In the illustrated embodiment,
there are six of these mounting screws and the head of each screw is
located in a screw recess 158 formed in the mounting flange that extends
around the locating ring 140.

[0049] Shown also in FIG. 10 is the plastics injection passage system that
extends through the valve gate nozzle. As in the embodiment of FIGS. 1
and 2, the injection passage splits into two sub-passageways 102, 104 in
the actuator section of the valve gate nozzle. These two sub-passageways
extend along opposite sides of the actuator chamber 30 and are located in
the wall forming the actuator chamber. In the nozzle shaft 72, these two
sub-passageways converge at 102' and 104'. The converging sections meet
at the annular passage 20 that surrounds the valve pin. It is also
possible to have only one passageway extending around one side of the
actuator chamber. Also visible in FIG. 11 is a thermal couple 160 which
is used to monitor the temperature of the nozzle shaft in a manner known
per se. Thermal couples can be provided elsewhere on the valve gate as
well in a known manner.

[0050] Shown in FIGS. 9 to 11 is a wiper seal assembly indicated generally
at 170. This assembly through which the valve pin 24 extends is mounted
in the top end of the nozzle shaft 72. The wiper seal assembly can
include one seal ring 172 or several seal rings that are held in position
in a counterbore and in a retainer housing 174 by a set screw 176. The
set screw is threaded into an opening formed in the top of the nozzle
shaft 72 so as to engage the top of the retainer housing 174. The purpose
of the wiper seal assembly is to provide a zero gap precision fit with
the valve pin which is slidable therein. The wiper seal provides a tight
fitting seal that allows the valve pin to move in the axial direction
between the open and closed positions while at the same time preventing
leakage of plastics melt past the seal. Because the wiper seal is
installed in a high temperature operating environment inside the heated
nozzle body, the seal is selected to withstand the plastic processing
temperature of thermal plastics material normally ranged between
200° C. and 300° C. (309° F. to 575° F.) The
selected seal or seals desirably provide good lubricity, elasticity and a
temperature resistance of more than 300° C. A suitable material
for the wiper seal is polyimide with molybdenum disulfide filler or
polytetrafluoroethylene (PTFE) with boron nitrite filler. A wiper seal of
this material can have a temperature rating of 600° F. for long
term use and up to 900° F. for medium term use. Thus such seals
are suitable for the entire processing temperature range of standard
thermoplastic materials. The wiper seal assembly 170 can also be used
around the valve pins in the hotrunner system of FIGS. 1 and 2. Possible
base materials for the wiper seal include a high temperature resistant
polymer such as PI (polyimide), PEI (polyether ether imide), or PEEK
(polyether ether ketone) with the base material containing a filler to
reduce friction. A typical filler for this purpose is the aforementioned
PTFE or molybdenum disulfide (MoS2). The elastomeric wiper seal can
be installed in its holding cavity by being pushed in under a pre-load.
The internal diameter of this seal can be five to ten microns smaller
than the diameter of the pin, thus ensuring no gap between the pin and
the seal. The wiper seal will expand as it is heated but is able to
permit the required pin movement.

[0051] The valve pin movement is guided in the nozzle shaft by a guide
passage 74. In an exemplary embodiment of the valve gate this guide
passage is formed by a machined bore made to close tolerances so that a
micro-gap is formed between the valve pin 24 and the machined bore. This
micro-gap which can be in the order of several microns may allow polymer
molecules, pigments and gases to escape to the outside of the passageways
provided for the flow of hot plastics material. This is due to the high
temperature of the hot plastics melt, the high injection pressure used to
deliver the plastics melt to the valve gate and the valve pin stroke.
This escape of material can cause over time maintenance issues inside the
injection mold, but this escape can be prevented by the use of the above
described wiper seal assembly. As with the micro-gap between the piston
and the actuator chamber wall, the micro-gap between the valve pin and
the machined bore is measured with the pin and the bore contacting each
other on one side. The micro-gap is the distance between the side of the
pin and the bore wall at the point diametrically opposite the contact
point.

[0052] In addition to the provision of the micro-gap between the pin and
the guide passage wall and the provision of the wiper seal assembly, a
transversely extending additional passage 180 can be provided in the
nozzle shaft 72 near its upper end. As shown in FIG. 9, this additional
passage intersects the guide passage (including the guide passage that
extends through the wiper seal assembly) at a location spaced from the
actuator chamber 30. The passage 180 allows gases or plastics melt
residue that has entered into the bore to escape. The passage 180 can be
described as a decompression bore. It should be noted that it is also
possible to employ this decompression bore even in a valve gate nozzle
having no wiper seal assembly that extends about the valve pin. Note also
that pressurized air in the actuator chamber itself can pass through the
micro-gap around the valve pin (particularly in the case where no wiper
seal assembly is used) and the escaping air flow provides self-cleaning
of the annular gap that extends between the actuator chamber and the
passage 180. Note that the micro-gap around the valve pin in an exemplary
embodiment of the valve gate nozzle is between one and ten microns and is
dependent in part on the diameter of the pin itself.

[0053] FIGS. 12 and 13 illustrate another form of hotrunner system
constructed in accordance with the present disclosure. This hotrunner
system, which is indicated generally by reference 190, has a centrally
located manifold plate 192 which is located in an air containing cavity
194. Again, this manifold has an inlet for receiving melted plastics
material from a plasticizer unit (not shown) and a plastics feed conduit
196 connected to this inlet. As in the above described versions of
hotrunner systems, the manifold is adapted for operation at a desired
elevated temperature suitable for the flow of the melted plastics
material through the manifold without undesirable degradation. The
hotrunner system has a mold cavity plate 198 and two manifold mold plates
200, 202 which are held against one another under pressure applied by the
mold machine. The cavity 194 is formed between the two mold plates, only
portions of which are shown in FIG. 13. The mold cavity plate is formed
with two or more stepped cavities 204 in each of which is mounted a
portion of a respective one of injection apparatus in the form of nozzle
members 206. In this particular hotrunner system 190, there are two or
more nozzle members 206 mounted on one side of the manifold plate 192 and
each has a longitudinal axis indicated at A in FIG. 13. Each nozzle
member has an injection passage operatively connected to a respective
outlet of the feed conduit of the manifold and extending to a nozzle tip
208. A section of this passage which surrounds a bottom portion of a
valve pin can be seen at 210. This portion, which extends along the
longitudinal axis A, is connected to a sloping passage section 212 of
which there is only one in this version of the nozzle member. An elongate
valve pin 212 extends the length of its respective nozzle member and also
extends into the manifold 192 in which are formed actuator chambers 214.
As in the previous embodiments, each valve pin extends through a
respective guide passage 216 and is movable therein between an open
position (shown in FIG. 13) at which melted plastics material can flow
from the respective nozzle tip into an injection mold 220 and a closed
position (shown in FIG. 12) which stops flow from the nozzle tip.

[0054] This hotrunner system also has a plurality of pistons 222, each
connected to a rear end of a respective one of the valve pins, slidably
mounted in an associated one of the actuator chambers 214, and adapted to
move the respective valve pin between the open and closed positions by
means of fluid pressure in the associated actuator chamber. Pressurized
air can be delivered through the manifold to the actuator chamber through
air passageways indicated at 224 and 226.

[0055] Because of the high operating temperature of the manifold plate
192, it is necessary to avoid the use of seals between the peripheral
wall of each piston and the surrounding cylindrical wall of the actuator
chamber formed in the manifold. Accordingly, the pistons 222 and the
cylindrical walls forming the actuator chambers are machined to close
tolerances so as to form a micro gap between a peripheral wall of each
piston and the adjacent cylindrical wall in the range of 1 to 10 microns.
In this way, each piston 222 and its associated actuator chamber 214
provide a valve pin actuator able to operate within plastic injection
temperatures ranging between 200° C. and 400° C.

[0056] In an exemplary form of this hotrunner system, each guide passage
216 comprises a machined bore and a micro gap is formed between each
valve pin 212 and its respective machined bore. As explained above, the
provision of such a micro gap helps to prevent hot melted plastics
material in the respective nozzle member from passing through the micro
gap into the adjacent actuator chamber under normal operating conditions.
The above described wiper seal can be provided adjacent to or along the
guide passage 212.

[0057] With particular reference to FIG. 13, it will be seen that each
nozzle member 206 is clamped between and held in position by the manifold
plate 192 and the mold plate 202. A circular opening can be provided at
230 in the mold plate and the nozzle member extends through this opening.
The nozzle member has a wider rear section 232 which fits snugly into an
annular recess formed on an inner surface of a mold plate. The narrower
section of the nozzle member extends into its respective mold insert 42,
which is mounted in the stepped cavity 204.

[0058] FIG. 14 illustrates yet another form of hotrunner system
constructed in accordance with the present disclosure, this system being
indicated generally at 240. This system can be constructed in a manner
similar to the above described hotrunner system 190 shown in FIGS. 12 and
13 except for the differences noted hereinafter. This hotrunner system
has a central manifold plate 242, which is mounted in a central air
cavity formed by manifold mold plates 244 and 246. The hotrunner molding
machine of FIGS. 14 has two cavity plates 248, 250, each of which is
formed with a plurality of stepped cavities 204. In each cavity is
mounted a portion of a nozzle member 206. The manifold mold plates are
held against one another and the pressure applied through the two cavity
plates.

[0059] The manifold plate 242 forms at least one large actuator chamber
252. A pair of pistons 222 are mounted in each large actuator chamber and
each of these are connected to the rear end of a respective valve pin
212.

[0060] It will be seen that in the embodiment of FIGS. 14, unlike that of
FIGS. 12 and 13, the nozzle members 206 are mounted on two opposite sides
of the manifold, these sides being indicated at 254 and 256. Each nozzle
member 206 on one side is aligned in a back-to-back manner with a
respective nozzle member on the opposite side and a single large actuator
chamber 252 can be provided for each pair of pistons 222 for the aligned
nozzle members. Thus, it will be appreciated that the aligned valve pins
of each pair of aligned nozzle members move simultaneously between their
respective open and closed positions. Alternatively, a separate actuator
chamber can be formed in the manifold for each of the pistons 222.

[0061] As in the embodiment of FIGS. 12 and 13, in the hotrunner system
240, each valve pin is movable in a longitudinal guide passage 216, which
is in the form of a machined bore. A micro gap is formed between each
valve pin and its respective machined bore so that, under normal
hotrunner system operating conditions, hot melted plastics material in
each nozzle member is prevented from passing through the micro gap into
the adjacent actuator chamber.

[0062] A further detail shown in FIG. 14 is the provision of the
additional passage 260 formed in each nozzle member 206 close to the end
of the nozzle member that is pressed against the manifold plate. This
transverse passage serves the same purpose as the passage 180 in the
injection apparatus of FIG. 9. As shown, the additional passage
intersects the guide passage 216 and it allows gasses or plastic melt
residue that has entered into the guide passage to escape, in other words
this passage serves as a decompression bore. Pressurized air in the
actuator chamber 252 can pass through the micro gap around the valve pin.
Any such escaping air provides self-cleaning of the annular gap that
extends between the actuator chamber and the passage 260.

[0063] The machined cylindrical wall for each actuator chamber 252 can
also be provided with a hardened surface in the manner described above.
In particular, the wall of the actuator chamber 214 or 252 can have a
machined nitride surface, which is harder than the peripheral wall of the
piston. Alternate possible surfaces of the piston and/or the wall of the
actuator chamber formed in the manifold plate are surfaces with physical
vapour deposition (PVD) or CVD enhancement. Also the cylindrical walls of
the actuator chambers in the manifold plate can be impregnated with a
high temperature dry lubricant in a manner known per se as explained
above.

[0064] In the two embodiments shown in FIGS. 12 to 14 the stack height of
the manifold and nozzle assembly is more compact and this allows for a
more compact injection mold. A reduced mold stack height benefits the
opening stroke of the mold for the injection of the plastic part.

[0065] FIGS. 15 and 16 illustrate an alternate form of nozzle valve gate
apparatus according to the present disclosure, this apparatus indicated
generally by reference 268. The apparatus 268 is for injection hot
plastics material into an injection mold (not shown) for molding a
plastics product or part. The valve gate apparatus includes an actuator
mechanism indicated generally at 271 which per se can be of standard
construction and which includes an actuator chamber and a piston slidably
mounted in the actuator chamber. A piston 273 is movable by fluid
pressure in actuator chamber 275 during use of the valve gate apparatus.
It will be understood that because the actuator mechanism is spaced apart
from a hotrunner manifold 270 by means of a stand off sleeve 276 and
because hot plastics melt does not flow through this standard actuator,
the actuator mechanism can be kept at a relatively low temperature and
therefore known seals can be provided between the piston and the
cylindrical wall of the actuator housing 274. The sleeve creates a
thermal barrier between the manifold and the actuator 271. The upper end
of the valve pin 304 is connected in a known manner to the actuator
piston 273. Visible in FIG. 15 are input/output ports 290, 292 which
deliver pressurized air or gas to or from the actuator chamber in order
to operate the piston and move the valve pin between its open and closed
positions. The valve pin is shown in its closed position in FIG. 15 and,
in this position, the injection aperture 288 is closed.

[0066] Heaters for the manifold are indicated at 306 and 308 and these are
imbedded in the top and bottom surfaces of the manifold. The manifold has
a plastics feed conduit 310 that is able to deliver hot plastics melt to
a plurality of injection nozzles 312 only one of which is shown. The
injection nozzle forms an annular injection passage 314 that extends
around the valve pin and that is connected to the feed conduit 310 by a
short connecting branch 284 of the feed conduit. Extending around the
injection nozzle 312 is a cylindrical nozzle heater 316 similar to the
heater 86. The injection nozzle and the heater extend through a passage
320 formed in mold plate 300. Attached to the bottom of the mold plate
300 is a cavity plate 302 which can be detachably connected by means of
bolts (not shown) extending through bolt passages 322. Cavities are
formed in the plate 302 to accommodate a plurality of annular mold
sections 324 only one of which is shown. These sections can each be
bolted to the cavity plate by bolts (not shown) extending through bolt
holes 326. The nozzle tip 286 is held rigidly in place by the mold
section. A cavity for the manifold is formed both by the mold plate 300
and an upper mold plate 330.

[0067] The nozzle valve gate apparatus 268 is also provided with an
elastomeric wiper seal indicated at 332 (see FIG. 16). This seal is
mounted at the bottom end of a wiper seal bushing 280 which can also be
described as a retainer. Again this seal extends around and slidably
engages the valve pin 304 and the seal is capable of withstanding
injection nozzle operating temperatures of at least 200° C. and in
one exemplary version temperatures of at least 300° C. It will be
seen that in this nozzle valve gate apparatus the seal is mounted in the
heatable manifold 270 which is part of the overall injection arrangement.
As can be seen from FIG. 16, the wiper seal is separated from the
injection passage including the feed conduit 310 and the connecting
branch 284 by a machined guide bore indicated at 282. In particularly a
micro gap is provided between the valve pin and guide bore 282 and a zero
gap is formed between the wiper seal 332 and the valve pin. In an
exemplary version of this valve gate apparatus, the micro gap is in the
range of 1 to 10 microns and the wiper seal is formed with and contains a
lubricating filler. In one embodiment, the wiper seal is made of
polyimide and is self lubricating.

[0068] As can be seen clearly from FIG. 16, the wiper seal 332 is mounted
in a cavity 334 formed in the manifold. In particular the annular bushing
or retainer 280 extends into this cavity and is mounted in the cavity in
a snug fitting manner. The bushing extends around the circumference of
the wiper seal and fixedly holds the seal in the cavity. The bushing also
extends through a mounting plate 278 formed with a central hole for the
bushing and holding the bushing in place. The plate 278 is attached to
the manifold by four screws (not shown). The plate provides a preload on
the annular shoulder of bushing 280. The plate also creates an air gap at
301 to provide a thermal barrier. Another annular air gap can be provided
at 303 around the upper portion of the bushing 280. The cylindrical hole
305 in the pate 278 can be provided with a diameter slightly greater than
the upper section of the bushing which makes insertion of the bushing
into the plate easier. However the top part of the hole 305 forms a tight
fit with the bushing in order to prevent any movement of the bushing
during use.

[0069] The machined bore at 282 and the guide pin are partnered and
interact to provide a very close cylindrical slide fit with the
aforementioned micro gap of 1 to 10 microns. As indicated previously, the
hot melt flowing through the manifold can be at high pressure and the
moving stroke or the valve pin can be between 5 and 20 mms. In this
situation, small amounts of plastic material, gases and melt additives
can escape through the micro gap at the bore 282 and, unless remedied,
this leaking material can cause mold maintenance, production downtime and
plastic part quality issues. Such leaks will over time result in
malfunction of the valve pin and the actuator. However, because of the
zero gap provided by the wiper seal around the valve pin, no pressurized
melt will escape past the wiper seal to the outside of the manifold,

[0070] While the present invention has been illustrated and described as
embodied in exemplary embodiments, e.g. embodiments having particular
utility for injection apparatus and machines for injecting plastics
material from a plasticizer unit into an injection mold, it is to be
understood that the present invention is not limited to the details shown
herein, since it will be understood that various omissions,
modifications, substitutions and changes in the forms and details of the
disclosed systems and nozzle valve gates and their operation may be made
by those skilled in the art without departing in any way from the spirit
and scope of the present invention. For example, those of ordinary skill
in the art will readily adapt to present disclosure for various other
applications without departing from the spirit or scope of the present
invention.

Patent applications by Harald Schmidt, Georgetown CA

Patent applications by Mold Hotrunner Solutions, Inc.

Patent applications in class With accumulator, trap chamber, or serially arranged valves between charger and mold

Patent applications in all subclasses With accumulator, trap chamber, or serially arranged valves between charger and mold